Determination of pore structure characteristics of filtration cartridges as a function of cartridge length

ABSTRACT

A method for determining pore structure characteristics of a filtration cartridge includes the steps of placing a porometry test location isolating device in sealing contact with the filtration cartridge at a desired test location, increasing the porometer test gas pressure until the test gas flows through the cartridge at the test location, measuring the flow rate of the test gas through the test location as a function of differential pressure, reducing the test gas pressure to atmospheric pressure, wetting the test location with a wetting liquid, increasing the test gas pressure again until the test gas flows through the cartridge at the test location, measuring differential gas pressure and gas flow rates through the test location, and converting the measured gas flow rates and differential pressures into through pore throat diameters, largest through pore throat diameter, mean flow through pore throat diameter, pore distribution, and gas permeability of the cartridge.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to the field of flow porometry. Moreparticularly, the invention pertains to a method and apparatus for theuse of flow porometry to determine the pore structure characteristics offiltration cartridges as a function of the cartridge length.

2. Description of Related Art

Filtration cartridges are workhorses of modern industry. Filtrationcartridges essentially are used for the separation of suspended solidsfrom liquids and/or gases. Numerous applications of filtrationcartridges are found in a wide range of industries, includingbiotechnology, chemical, pharmaceutical, food and drink, medical,electronic, automobile, and the construction industries. A wide varietyof tasks are performed by filtration cartridges, such as, for example,filtration of bacteria, pollen and cells from bodily fluids,purification of chemicals, detoxification of waste water, removal ofheavy ions from water for use in the electronic industry, purificationof pharmaceutical products, removal of pathogens and solids from softdrinks, and removal of excess water from slurries.

The performance of the filtration media and the ability to separatesolids from fluids are determined by the pore structure characteristicsof the filtration media. Relevant pore structure characteristics offiltration media include, for example, through pore throat diameters,the largest through pore throat diameter, mean flow through pore throatdiameter, pore distribution, and fluid permeability.

For purposes of product development and/or quality control, for example,it is often desirable to measure such pore structure characteristics offiltration cartridges. Such pore structure characteristics of filtrationmedia generally can be accurately measured in a flow porometer, such asthe Capillary Flow Porometer of Porous Materials, Inc. (See Akshaya Jenaand Krishna Gupta, Characterization of Pore Structure of FiltrationMedia, Fluid/Particle Separation Journal, Vol. 14, No. 3, 2002, pp.227-241, and Akshaya Jena and Krishna Gupta, Liquid Extrusion Techniquesfor Pore Structure Evaluation of Nonwovens, International NonwovensJournal, Vol. 12, No. 3. 2003, pp. 45-53, the complete disclosures ofwhich are hereby incorporated herein by reference in their entireties).Porous Materials, Inc. is a pioneer in the field of flow porometry andhas obtained several patents in the field, including U.S. Pat. No.6,766,257, which describes PMI Capillary Flow Porometry, and U.S. Pat.No. 6,684,685, the complete disclosures of which are hereby incorporatedherein by reference in their entireties.

U.S. Pat. No. 6,684,685 discloses a liquid extrusion porosimeter andmethod for evaluating porosity characteristics (specifically, porevolume, pore distribution and liquid permeability) of porous materials,such as filtration media. The porosimeter includes a fluid reservoirlocated below the sample, and a penetrometer comprising a vessel thatcatches any fluid displaced from the reservoir of fluid, wherein a levelof fluid rises in the penetrometer when additional fluid enters thepenetrometer. The sample is preferably wetted, with the same type offluid that is in the reservoir, prior to placing the sample on theporosimeter. The porosimeter preferably also includes a membrane locatedbetween the sample and the reservoir of fluid. The membrane has poreswith a size smaller than any of the sample pores. Pore volume of thesample is determined by measuring the change in fluid level in thepenetrometer after pressure, which is above the bubble point pressure ofthe sample but below the bubble point pressure of the membrane, isapplied to the sample. Permeability is measured by measuring rate offlow while the liquid level is above the sample.

The PMI Capillary Flow Porometer is a completely automated instrument.It measures pressures of the test gas accurately. It increases pressurein small increments, allows the system to equilibrate, and then recordsthe increase in pressure. The flow rate through the sample is alsomeasured accurately. Pressures can be raised to high values or reducedfrom high values to very low values. The porometer delivers thecompressed gas through a tube to the sample chamber, which can bedesigned to hold samples of various sizes and shapes.

The technique of flow porometry is based on the simple principle that awetting liquid spontaneously fills the pores of filtration media. Forthe wetting liquid, the surface free energy of the filtration media withthe liquid is less than the surface free energy of the filtration mediawith air. Therefore, filling of the pores by the wetting liquid isaccompanied by a decrease in free energy and the filling process isspontaneous. The wetting liquid cannot spontaneously flow out of thepores, however, it can be removed from the pores by a pressurizednon-reacting gas.

The gas pressure needed to displace a wetting liquid from a pore isrelated to the pore diameter, as follows:p=4γ cos θ/D  (1)where, p is the differential gas pressure on the wetting liquid in thepore, γ is the surface tension of the wetting liquid, θ is the contactangle of the wetting liquid with the filtration media, and D is the porediameter. The test involves measurement of gas flow rates through a drysample as a function of differential pressure. The differential pressureis reduced to zero, the sample is wetted with a wetting liquid, and gasflow rates through the wet sample are measured as a function ofdifferential pressure. FIG. 1 shows a schematic plot of gas flow ratesthrough a sample in dry and wet conditions, and FIG. 2 shows a graph ofpore size distribution.

The wet curve generated by the wet sample shows no gas flow withincrease in differential pressure at the beginning of the test, becauseall of the pores are filled with the wetting liquid. The first pore tobe emptied at the lowest pressure is the largest pore (see Equation 1above). The differential pressure that initiates gas flow through a wetsample yields the largest through pore diameter (FIG. 1).

The diameter of a pore can change along the pore path. The differentialgas pressure that is sufficient to displace liquid from the pore throatcan completely empty the pore and initiate gas flow. Therefore, the porediameter computed from the measured differential pressure yields thethrough pore throat diameter. The measured largest pore diameter is thelargest through pore throat diameter. The dry curve is produced by thedry sample. The half-dry curve represents computed data that yield halfof the gas flow rate through the dry sample at a given differentialpressure. The differential pressure at which the wet curve and thehalf-dry curve have the same flow rates yields the mean flow throughpore throat diameter. The mean flow pore diameter is such that half ofthe flow is through pores smaller than the mean flow pore and the restof the flow is through pores larger than the mean flow pore. The ratioof flow rates through the wet sample and the dry sample also yields flowdistribution over pore diameter (FIGS. 1 and 2). This distribution hasbeen shown to be close to pore fraction distribution (See A. K. Jena andK. M. Gupta, Pore Size Distribution in Porous Materials, Proceedings ofInternational Conference Filtration 99, November 3-4, Chicago, INDA,1999). Gas permeability is computed from measured gas flow rates throughthe dry sample using Darcy's law (See P. C. Carman, Flow of Gasesthrough Porous Media, Academic Press, 1956).

Characteristics of filtration media that can be measured accurately byflow porometry include, for example, the constricted pore diameter, thelargest pore diameter, the mean flow pore diameter, pore distribution,gas permeability, liquid permeability, envelope surface area and effectsof operational variables, such as temperature, pressure, chemicalenvironment and stress. Demonstrated applications of flow porometryinclude analysis of pore characteristics in the thickness direction,pore characteristics in the x-y plane, properties of individual layersof multi-layered products determined in-situ without separating thelayers, and evaluation of properties without cutting samples anddamaging the products. See, e.g., U.S. Pat. Nos. 6,766,257, 6,789,410,6,845,651, and 7,040,141.

U.S. Pat. No. 6,766,257 discloses a method of determining the porestructure of the individual layers in a multi-layered composite porousmaterial, including the steps of providing a sample of a multi-layeredporous material, sealing the sample in suitable test chamber, fillingthe pores of the sample material with a wetting liquid, such that theliquid/sample surface free energy is less than the gas/sample surfacefree energy, using a non-reacting gas to apply pressure to one side ofthe sample sealed in the test chamber, increasing the gas pressuregradually, so as to displace the liquid from the pores, increasing gasflow through the sample, measuring the pressure at which liquid flowsfrom each successive layer of the sample material, and calculating thepore structure using an equation selected from the group consisting ofp=γ(dS/dV), D=4γ/p, and f=−d[100(F_(w)/F_(d))]/dD.

U.S. Pat. No. 6,789,410 discloses a porosimeter that includes apressurizable sample chamber with a membrane located directly below thesample. The membrane pores have a smaller size than any of the samplepores of interest. A fluid reservoir is located below the membrane suchthat the reservoir and the membrane form a seal. In operation, as fluidenters the fluid reservoir through the membrane or a reservoir inlet,fluid already in the fluid reservoir is displaced through a reservoirexit. An inlet in a fluid displacement reservoir receives the fluiddisplaced from the fluid reservoir. A recirculation line receives fluidfrom the exit of the fluid displacement reservoir and circulates thefluid into the inlet of the fluid reservoir. In a preferred embodiment,a pump recirculates the fluid through the recirculation line. Fluidreturned to the reservoir circulates over the bottom of the membrane,and sweeps air bubbles out of the reservoir.

U.S. Pat. No. 6,845,651 discloses a method and apparatus for determiningsurface area and pore distribution of a sample. A pressurizable samplechamber of known volume holds a sample with unknown porositycharacteristics. The sample chamber has a known pressure (or vacuum). Aflow controller preferably controls the flow of the pure gas to beadsorbed by the sample in the sample chamber. A pressure monitorpreferably monitors the pressure in the sample chamber. Once thepressure approaches a target pressure, the flow controller is closed.The pressure monitor continues to monitor the pressure until it stopschanging when an equilibrium is attained. The amount of gas introducedinto the system through the flow controller and the volume and finalpressure of the sample chamber are used to calculate the amount of gasadsorbed. This calculation is subsequently used to determine theporosity characteristics of the sample. Some of these characteristicsinclude, but are not limited to, pore distribution and surface area.

U.S. Pat. No. 7,040,141 discloses a method and apparatus for determiningporosity characteristics of a sample having a plurality of pores,located within a pressurizable chamber. The sample divides the chamberinto a first volume and a second volume. A known amount of vapor isintroduced into the first volume and the second volume at the samepressure (P_(x)). After equilibrium is reached, pressure and decrease involume of vapor are measured. Pore diameter and pore volume arecalculated. A pressure differential is created between the two volumes,and the pressure change is monitored after the pressure differential isintroduced. In a preferred embodiment, the pressure is increased in thefirst volume by a small percentage (ΔP_(x)), and the pressure change onboth sides of the sample is monitored after the pressure increase. Theflow rate of the vapor is calculated using the pressure change. Thesesteps are preferably repeated. The pore distribution in the sample ispreferably calculated from the flow rates.

Although there are known methods and apparatus that are intended to aidin the analysis of pore structure characteristics of filtration media,one problem with the known methods is that they are not well-suited foranalyzing the pore structure characteristics of filtration cartridges asa function of cartridge length. Thus, the known methods do not allow thepore structure of a filtration cartridge to be determined at a selectedlocation along the length of the cartridge, and do not allow the porestructure of the cartridge to be evaluated as a function of cartridgelength.

Thus, there is a need in the art for a method and apparatus for usingflow porometry to determine the pore structure characteristics offiltration cartridges as a function of cartridge length.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for using flowporometry to determine the pore structure characteristics of filtrationcartridges as a function of cartridge length. The apparatus according tothe invention provides several porometry test location isolating devicesdesigned for using a flow porometer to determine the pore structurecharacteristics at any location along the length of a filtrationcartridge, including means for directing the flow of a pressurized testgas through a preselected test location along the length of thefiltration cartridge. The test location isolating devices easily areoperatively connected to a porometer to enhance its ability to determinepore structure characteristics of a cartridge as a function of itslength. Various alternative embodiments include test location isolatingdevices provided as inserts, rings, and sleeves that slidingly engageeither the inner or outer surface of the filtration cartridge and directthe test gas through the selected test location along the length of thecartridge.

Briefly stated, a method according to the invention provides fordetermining the pore structure characteristics of a filtrationcartridge, including the steps of placing a porometry test locationisolating device in sealing contact with the filtration cartridge at adesired test location, increasing the porometer test gas pressure untilthe test gas flows through the cartridge at the test location, measuringthe flow rate of the test gas through the test location as a function ofdifferential pressure, reducing the test gas pressure to atmosphericpressure, wetting the test location with a wetting liquid, increasingthe test gas pressure again until the test gas flows through thecartridge at the test location, measuring differential gas pressure andgas flow rates through the test location, and converting the measuredgas flow rates and differential pressures into through pore throatdiameters, largest through pore throat diameter, mean flow through porethroat diameter, pore distribution, and gas permeability of thecartridge.

In the preferred embodiment, the invention provides a porometry testlocation isolating device comprising an insert adapted to slidinglyengage the inner surface of the inner cylindrical bore of a filtrationcartridge. The apparatus includes a tubular member having a test gasinlet at its first end and a sealed second end, a plurality of radialgas channels arranged between the first and second ends of the tubularmember for directing flow of the pressurized test gas through thetubular member to the test location of the cartridge, and a pair ofO-rings seated within a pair of circumferential O-ring grooves arrangedbetween the radial gas channels and the first and second ends of thetubular member, the O-rings defining the test location and confiningflow of the pressurized test gas through the test location.

In an alternative embodiment, the invention provides a porometry testlocation isolating device comprising an insert adapted to slidinglyengage the inner surface of the cylindrical bore of a filtrationcartridge. The apparatus includes a tubular member having a test gasinlet at its first end and a sealed second end, a plurality of radialgas channels arranged between the first and second ends of the tubularmember for directing flow of the pressurized test gas through thetubular member to the test location of the cartridge, and a pair ofgaskets seated within a pair of circumferential gasket grooves arrangedbetween the radial gas channels and the first and second ends of thetubular member, the gaskets defining the test location and confiningflow of the pressurized test gas through the test location, and a pairof flexible members attached to the ends of the tubular member forpulling the insert through a filtration cartridge having an irregularshape or a bent or deformed cartridge.

In yet another alternative embodiment, the invention provides aporometry test location isolating device comprising a ring adapted toslidingly engage an outer surface of a cylindrical filtration cartridge.The apparatus includes a ring member having a groove within an innersurface thereof defining a central gas channel connected to a test gasinlet, the central gas channel being arranged to direct the flow of thetest gas through the ring member to the test location of the cartridge,and a pair of gaskets seated within a pair of gasket grooves arranged oneach side of the central gas channel, the gaskets defining the testlocation and confining flow of the pressurized test gas through the testlocation.

In still yet another alternative embodiment, the invention provides aporometry test location isolating device comprising a pair of sleevesadapted to slidingly engage an outer surface of a cylindrical filtrationcartridge. The apparatus includes a pair of tight fitting rubber sleevesslidingly engaged at each end of a filtration cartridge, the gap betweenthe rubber sleeves defining the test location and confining flow of thepressurized test gas through the test location, and a test gas inletlocated at an end of one of the sleeves, and a sealed end located at anend of the other of the sleeves, with the cartridge being arrangedbetween the sleeves.

The invention provides the advantage of enabling the analysis of thepore structure characteristics of filtration cartridges as a function ofcartridge length. Thus, the invention allows the pore structure of afiltration cartridge to be determined by flow porometry at any locationalong the length of the cartridge, and allows the pore structurecharacteristics of the cartridge to be evaluated as a function ofcartridge length. Furthermore, the invention provides means foremploying a quick scan along the length of a cartridge as an aid inidentifying the presence of major defects.

These and other features and advantages will become readily apparentfrom the following detailed description, which should be read inconjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are not necessarily to scale, with the emphasis insteadplaced upon the principles of the present invention. Additionally, eachof the embodiments depicted are but one of a number of possiblearrangements utilizing the fundamental concepts of the presentinvention. The drawings are briefly described as follows.

FIG. 1 shows a graph depicting various pore structure characteristicsmeasurable by flow porometry.

FIG. 2 shows a graph depicting pore size distribution.

FIG. 3 shows a transverse sectional view of a typical filtrationcartridge that can be analyzed by flow porometry in accordance with thepresent invention.

FIG. 4 shows a sectional view of a porometry test location isolatingdevice, according to an embodiment of the present invention, speciallyadapted to slide inside the cylindrical bore of a filtration cartridge.

FIG. 5 shows a porometry test location isolating device, according to analternative embodiment of the present invention, specially adapted forbeing pulled inside a filtration cartridge.

FIG. 6 shows a porometry test location isolating device, according toanother alternative embodiment of the present invention, comprising aring member specially adapted for sliding over the outside surface of afiltration cartridge.

FIG. 7 shows a porometry test location isolating device, according toanother alternative embodiment of the present invention, comprising apair of sleeves specially adapted for sliding over the outside surfaceof a filtration cartridge

FIG. 8 shows a porometry test location isolating device, according toyet another alternative embodiment of the present invention, speciallyadapted to slide inside the cylindrical bore of a filtration cartridge.

FIG. 9 shows a graph depicting porometry gas flow rates measured asfunctions of differential pressure through a portion of a filtrationcartridge at the center of its length, in accordance with the presentinvention

FIG. 10 shows a graph depicting pore distribution in the center of thelength of the filtration cartridge of FIG. 9, in accordance with thepresent invention.

FIG. 11 shows a graph depicting gas flow rates through the center andthe two ends of a long filtration cartridge, in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description relates to certain preferred embodiments ofapparatus and methods for using flow porometry to determine the porestructure characteristics of filtration cartridges as a function ofcartridge length. It will be readily apparent that numerous variationsand modifications other than those specifically indicated will bereadily apparent to those of sufficient skill in the art. In addition,certain terms are used throughout the discussion in order to provide aconvenient frame of reference with regard to the accompanying drawings,such as “inside”, “outside”, and the like. Such terms are not intendedto be specifically limiting of the invention, except where so indicatedin the claims.

Filtration cartridge product development ideally requires measurement ofpore structure characteristics of complete filtration cartridges fordesign and performance evaluation. Important pore structurecharacteristics required for filtration cartridges include through-porethroat diameters, the bubble point pore diameter, mean flow porediameter, and pore distribution. All of these characteristics can bemeasured by capillary flow porometry. However, testing of a completefilter cartridge by capillary flow porometry is a major challenge,because of the high gas flow rates through large cartridges, large sizeof the sample holder, need for accurate measurement of pressure drop,and requirement of sufficient supply of gas for a reasonable time.

The pore structure characteristic of an entire filter cartridge can bemeasured by a porometer, provided that the porometer is capable ofaccommodating the complete cartridge in the sample chamber, producingvery high flow rates of gas for large cartridges, accurately measuringflow rates and pressure drops in such a system, and supplying adequateamount of gas for the test duration. The PMI Complete Filter CartridgeAnalyzer has all of these features and we have recently shown that it iscapable of measuring the relevant pore structure characteristics of anentire filtration cartridge (Akshaya Jena and Krishna Gupta, PoreStructure Characteristics and Gas Permeability of Complete FilterCartridges, Proceedings, Filtech, Germany, Oct. 11-13, 2005).

Limitations of Available Techniques: Filter cartridges are often long,so that their output is high. The pore structure of a long cartridgenormally is not uniform. Large size pores, increased or decreasedconcentration of pores, and defects produced during manufacturing due tofactors such as non-uniform distribution of powders or fibers,non-uniform compaction, and improper sintering or hot pressing may bepresent at a number of locations along the length of a long cartridge.However, the presence of such structural abnormality is not usuallyrevealed, when the entire cartridge is tested as a whole. Thus, theperformance of a cartridge may be poor, even though the overall porestructure of the entire cartridge containing defects along its lengthappears to be satisfactory. It is, therefore, imperative to be able tomeasure the pore structure characteristics of a complete filtrationcartridge at various locations along its length, to eliminate cartridgeswith unacceptable defects, and/or make changes in processing techniquesused for the manufacture of the cartridges, so as to avoid or minimizesuch defects. However, due to the foregoing problems, currentlyavailable methods do not allow for the measurement of the pore structurecharacteristics of a complete filtration cartridge at various locationsalong its length.

In the present invention, we disclose novel apparatus and methods thathave been developed to determine the pore structure at various locationsalong the length of a filtration cartridge, using a flow porometer(i.e., the PMI Capillary Flow Porometer). The methods and apparatusdisclosed herein have been successfully used to measure various relevantcharacteristics of through pores, including throat diameters, largestthroat diameter, mean flow pore throat diameter, pore distribution, andpermeability.

Equipment: The typical filtration cartridge (FIG. 3) is a hollowcylindrical shape with a porous wall and a cross-section that normallyis circular. Fluids (liquid or gas) pass through the pores, while solidparticles in the fluid are held back by the pores. The fluid moveseither from the inside to the outside or from the outside to the inside.

In order to test a selected location on the cartridge, we devisedmethods and specialized apparatus to permit flow of the test gas onlythrough a selected test location of the filter. These techniquesgenerally involve the use of specially designed test location isolatingdevices, such as inserts, rings, or sleeves that slide either inside oroutside the cartridge, several examples of which are described below.

Referring now to FIG. 4, a porometry test location isolating device 20according to an embodiment of the present invention is shown, speciallyadapted to slide inside the cylindrical bore 101 of a filtrationcartridge 10. The test location isolating insert 20 comprises a tubularmember 200 having a test gas inlet 201 at its first end and a sealedsecond end 202. In roughly the central region of the length of theinsert, a plurality of radial gas channels 203 is arranged between thefirst and second ends 201, 202 of the tubular member 200, extending fromthe inner central bore 204 of the insert to the outside of the insertfor directing flow of the pressurized test gas through the tubularmember to the test location of the cartridge. FIG. 4 shows three radialgas channels (the fourth being obscured in the drawing), however, thenumber can vary. Two O-rings 205 a, 205 b are seated within the twocircumferential O-ring grooves 206 a, 206 b on each side of the radialgas channels 203. The O-rings 205 a, 205 b effectively define the testlocation by confining the flow of the pressurized test gas through thearea between the O-rings. A pair of end tubes 207 is threaded to theends 201, 202 of the tubular member 200 to make airtight O-ring sealswith the tubular member. Compressed test gas is introduced through thetest gas inlet 201 and into the central bore 204, preferably via one ofthe end tubes 207 a. The free end of the other tube 207 b is sealed toprevent escape of the test gas.

The tube with sealed end 207 b is pushed inside the cartridge 10 untilthe desired test location is within the two circumferential O-rings 205a, 205 b on the tubular member 200. The O-rings 205 a, 205 b are suchthat air-tight seals are made between the tubular member 200 and theinner surface 102 of the cartridge 10, and that the insert 20 can bepushed from one end of the cartridge to the other for takingmeasurements at a particular location or taking multiple measurementsalong the length of the cartridge.

Different inserts can be designed, depending upon the shape orconfiguration of the filtration cartridge being tested, such that theinserts match the shape of the cartridge. FIG. 5 shows an alternativeembodiment of an insert similar to that of FIG. 4, but which is attachedto flexible end tubes 507 a, 507 b and employs gaskets 505 a, 505 b,instead of O-rings, within grooves 506 a, 506 b. This insert is designedto be more flexible, so that it can be pulled inside a bent cartridge(or a cartridge of unusual configuration) to the desired location fordetermination of the pore structure at a particular location or as afunction of cartridge length.

Referring now to FIG. 6, yet another alternative embodiment of a testlocation isolating device according to the invention is shown, speciallyadapted to slide over the outside of a filtration cartridge. The testlocation isolating ring 60 comprises a ring member 600 having a groovearound an inner surface thereof defining a central gas channel 604arranged to direct the flow of the test gas through the ring member tothe test location of the cartridge. The central gas channel 604 isconnected to a test gas inlet 601. A pair of gaskets 605 a, 605 b isseated within a pair of gasket grooves 606 a, 606 b arranged on eachside of the central gas channel 604. The gaskets 605 a, 605 beffectively define the test location by confining the flow of thepressurized test gas through the area between the gaskets. Rings ofvarious sizes can be designed to slide over the outside surface of thecartridge, and the desired test location on the cartridge can be broughtinside the ring for testing by sliding the cartridge inside the ring.

FIG. 7 shows still yet another alternative embodiment of a test locationisolating device according to the invention, specially adapted to slideover the outside of a filtration cartridge. In this embodiment, thefiltration cartridge 10 is inserted inside two tight fitting rubbersleeves 700 a, 700 b slidingly engaged over the ends of the cartridge.The gap between the rubber sleeves defines the test location byconfining the flow of the pressurized test gas through the area betweenthe sleeves. A test gas inlet 701 is located at an end of one of thesleeves, and a sealed end 702 is located at an end of the other of thesleeves, with the cartridge being arranged between the sleeves. Becausethe test area is exposed between the sleeves, this variation isparticularly suitable for cartridges having irregular cross-sections.

Test Procedure: The porometer is connected to the assembly of cartridgeand the test location isolating device, such as insert or ring orsleeve. The test location isolating device is moved either manually orautomatically by the porometer to the desired location. The porometerincreases the pressure of the test gas in small increments. The gas isconstrained to flow through the pores in the wall of the cartridge atthe desired location. Gas flow rate through the selected part of thecartridge is measured as a function of differential pressure. The gaspressure is then reduced to atmospheric pressure, the test area iswetted with a wetting liquid, and gas pressure is slowly increased.Differential gas pressure and gas flow rates through the wet locationare measured. The measured gas flow rates and differential pressures areconverted into through pore throat diameters, the largest through porethroat diameter, mean flow through pore throat diameter, poredistribution, and gas permeability of the selected annular location onthe cartridge wall. Pore structure characteristics at differentlocations are determined by moving the test location isolating device tothe desired location. The pore structure characteristics of thecartridge as a function of its length can be determined by performingtests at locations with increasing length. Any sudden variation in thepore structure may be obtained by measuring flow rate as a function oflength.

Example of Successful Application of the Invention: The invention wasused to determine the pore structure characteristics of a long cartridgeat different locations along its length. It had a wall thickness ofabout 3/16th inch. For this particular application, an insert made outof Teflon was used. The holes in the insert were about ⅛th inch indiameter and four in number. The circumferential O-rings were about7/16th inch apart. The stainless steel tubes attached to the insert werelong enough for the insert to be placed any where along the length ofthe cartridge. The arrangement is shown in FIG. 8. The loosely fittingplugs attached to the tubes extending from the insert at the two endswere for keeping the device straight and reducing any stress on thecartridge.

The fully automated PMI Capillary Flow Porometer was used to supplycompressed gas to the insert through the stainless steel tube andacquire the required data. The wetting liquid Galwick® (Propene,1,1,2,3,3,3-hexafluro oxidized, polymerized) was used to wet thecartridge. The measured flow rates through the part of the cartridge atits center in dry and wet conditions are shown in FIG. 9 as dry curveand wet curve respectively. The half-dry curve in the figure is computedto yield half of the flow rate through the dry sample at the samedifferential pressure.

Using these experimental data and using the procedure described above,the porometer computed the largest through pore throat diameter and themean flow through pore throat diameter as 227.6 μm and 30.62 μmrespectively in the center of the length of the cartridge. The poredistribution is given in terms of the distribution function, f, asfollows:f=−[d(F _(w) /F _(d))×100]/dD  (2)where F_(w) and F_(d) are gas flow through wet and dry samplesrespectively. The distribution curve is shown in FIG. 10. Thedistribution function is such that area under the function in any poresize range yields percentage gas flow through pores in that range. Thepore distribution is close to the pore number distribution.

Dry curve gave the gas flow rates through the dry sample. These flowrates were utilized to compute gas permeability of the sample usingDarcy's law.

Thus, all of the important pore structure characteristics at the centerof the length of the cartridge were measured. By sliding the insertinside the cartridge, pore structures in other locations also weremeasured. Pore structures in this cartridge changed appreciably withlength of the cartridge. For example, the mean flow through pore throatdiameters at the two ends of the cartridge were 5.9% and 12.5% lowerthan the mean flow through pore throat diameter in the center. Thevariation in the gas flow rates at the two ends and at the center of acartridge are shown in FIG. 11.

The present invention thus provides the advantage of enabling theanalysis of the pore structure characteristics of filtration cartridgesas a function of cartridge length. The invention allows the porestructure of a filtration cartridge to be determined by flow porometryat any location along the length of the cartridge, and allows the porestructure characteristics of the cartridge to be evaluated as a functionof cartridge length. Furthermore, the invention provides means foremploying a quick scan along the length of a cartridge as an aid inidentifying the presence of major defects, and has numerous applicationsin the development and manufacture of filtration cartridges.

It is to be understood that the architectural and operationalembodiments described herein are exemplary of a plurality of possiblearrangements to provide the same (or equivalent) general features,characteristics, and general system operation. Therefore, while therehave been described the currently preferred embodiments of the presentinvention, those skilled in the art will recognize that other andfurther modifications may be made, without departing from the spirit ofthe present invention, and it is intended to claim all modifications andvariations as fall within the scope of the appended claims.

Accordingly, it must further be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

What is claimed is:
 1. Test apparatus for using a flow porometer todetermine pore structure characteristics of at least a portion of afiltration cartridge, comprising a porometry test location isolatingdevice having means for directing flow of a pressurized test gas throughonly a preselected test location along the length of said filtrationcartridge, means for applying pressure in small increments to said testlocation, means for measuring differential pressures of said test gas,and means for measuring a rate of flow of said test gas through saidtest location, wherein said test location isolating device is selectedfrom the group consisting of inserts, rings, and sleeves that slidinglyengage either an inner or outer surface of said filtration cartridge anddirect said test gas through said test location of said cartridge, saidinsert comprising: a) a tubular member having a test gas inlet at afirst end thereof and a sealed second end; b) a plurality of radial gaschannels arranged between said first and second ends of said tubularmember for directing flow of said pressurized test gas through saidtubular member to said preselected test location of said cartridge; c) apair of O-rings seated within a pair of circumferential O-ring groovesarranged between said radial gas channels and said first and second endsof said tubular member, said O-rings defining said test location andconfining flow of said pressurized test gas through said test location;and d) a pair of flexible members attached to said ends of said tubularmember for pulling said insert through a filtration cartridge having anirregular shape or a bent or deformed cartridge.
 2. The apparatus ofclaim 1, wherein one of said flexible members attached to said tubularmember is a flexible tube member delivering said pressurized test gas tosaid test gas inlet.
 3. The apparatus of claim 2, operatively connectedto a flow porometer and/or means for manually or automatically movingsaid test location isolating device along the length of said filtrationcartridge.
 4. A method for using a flow porometer to determine porestructure characteristics of at least a portion of a filtrationcartridge, comprising the steps of: a) providing a flow porometer and afiltration cartridge for analysis; b) placing a porometry test locationisolating device of claim 1 in sealing contact with said filtrationcartridge at a preselected test location of said cartridge; c)increasing a test gas pressure of said porometer incrementally, suchthat said test gas is constrained to flow through said filtrationcartridge at said test location; d) measuring a flow rate of said testgas through said test location as a function of differential pressure;e) reducing said test gas pressure to atmospheric pressure; f) wettingsaid test location with a wetting liquid; g) increasing said test gaspressure again incrementally, such that said wetting liquid isconstrained to flow through said filtration cartridge at said testlocation; h) measuring differential gas pressure and gas flow ratesthrough said test location; and i) converting said measured gas flowrates and differential pressures into through pore throat diameters, thelargest through pore throat diameter, mean flow through pore throatdiameter, pore distribution, and gas permeability of said filtrationcartridge at said test location.
 5. The method of claim 4, furthercomprising the step of determining pore structure characteristics atdifferent test locations along the length of said filtration cartridgeby moving said test location isolating device to multiple testlocations, measuring flow rates and differential pressures at saidmultiple locations, and converting said measured gas flow rates anddifferential pressures at said multiple test locations.
 6. The method ofclaim 4, further comprising the step of determining pore structurecharacteristics of said filtration cartridge as a function of its lengthby performing tests at locations with increasing length.
 7. The methodof claim 4, further comprising the step of determining variation in porestructure by measuring flow rate as a function of length.
 8. The methodof claim 4, wherein said test location isolating device is moved to saidmultiple test locations manual or automatically by said flow porometer.9. The method of claim 4, comprising the step of determining said porestructure characteristics using the formula p=4γ cos θ/D orf=−[d(F_(w)/F_(d))×100]/dD.
 10. The method of claim 4, wherein saidporometry test location isolating device is selected from the groupconsisting of inserts, rings, and sleeves that slidingly engage eitheran inner or outer surface of said filtration cartridge and direct saidtest gas through said preselected test location of said cartridge. 11.The method of claim 4, wherein said test location isolating devicecomprises an insert adapted to slidingly engage an inner surface of acylindrical bore of said filtration cartridge, said insert comprising:a) a tubular member having a test gas inlet at a first end thereof and asealed second end; b) a plurality of radial gas channels arrangedbetween said first and second ends of said tubular member for directingflow of said pressurized test gas through said tubular member to saidpreselected test location of said cartridge; and c) a pair of O-ringsseated within a pair of circumferential O-ring grooves arranged betweensaid radial gas channels and said first and second ends of said tubularmember, said O-rings defining said test location and confining flow ofsaid pressurized test gas through said test location; and d) a pair offlexible members attached to said ends of said tubular member forpulling said insert through a filtration cartridge having an irregularshape or a bent or deformed cartridge.
 12. The method of claim 11,wherein one of said flexible members attached to said tubular member isa flexible tube member delivering said pressurized test gas to said testgas inlet.